Why are mutations uncommon in normal cells?
A)Only 25% of the genome codes for proteins, therefore the probability is low that a mutation would occur in a protein coding region.
B)Most mutations occur after DNA replication.
C)Many amino acids are coded for by more than one codon.
D)The mutation rate during DNA replication is 1 in 100 nucleotides.
E)The mutation rate during DNA replication is zero.

Question

Why are mutations uncommon in normal cells?  
A)Only 25% of the genome codes for proteins, therefore the probability is low that a mutation would occur in a protein coding region.
B)Most mutations occur after DNA replication.
C)Many amino acids are coded for by more than one codon.
D)The mutation rate during DNA replication is 1 in 100 nucleotides.
E)The mutation rate during DNA replication is zero.

Quizplus · Accepted Answer

Many amino acids have multiple codons that can code for them. Therefore, a mutation in a single nucleotide might not result in a change in the amino acid sequence of the protein. This decreases the likelihood of a significant impact on the protein function, reducing selective pressure against the mutation. Mutations also occur during DNA replication, but not often enough to make them common in normal cells. Finally, the genome coding for proteins is more than 25%, so choice A is incorrect. The mutation rate during DNA replication is not zero, so E is incorrect. The mutation rate during DNA replication is not 1 in 100 nucleotides, as stated in D.

Why Are Mutations Uncommon in Normal Cells